1. Field of the Invention
This invention relates to a platinum resistor for the measurement of temperatures, which functions as a temperature sensor.
2. Description of the Prior Art
Platinum is chemically stable and can be readily obtained with a high degree of purity. Moreover, the electrical resistance of platinum is greatly dependent upon temperatures. Thus, platinum has long been used as a material for temperature sensors, which is composed of an extremely thin platinum wire spirally wound around a mica insulator and a protective tube containing the said thin platinum wire therein. These temperature sensors are widely used as a resistor for the measurement of temperatures, the detailed specifications of which are given in Japanese Industrial Standard (JIS) C-1604, DIN 43760 and IEC Pub 751. This resistor for the measurement of temperatures is extremely accurate, but it contains such defects that:
(1) the mechanical strength is poor, PA0 (2) the production is time-consuming, PA0 (3) the product is large, and PA0 (4) the product is expensive. PA0 (1) a fine pattern is readily achieved, which makes possible miniaturization and high resistibility, so that an increase in sensitivity of the devices can be attained, PA0 (2) the mechanical strength is great, and PA0 (3) as these devices are produced in a wafer, quality control during production can be maintained and mass production becomes possible, so that the production cost can be reduced.
In order to eliminate these defects, resistors for the measurement of temperature using platinum in a thick or thin layer have been developed in recent years, and some are commercially available. However, the resistors for the measurement of temperatures including thick platinum layers are produced by a screen printing technique, causing problems in that the formation of a fine pattern of 100 .mu.m or less is difficult and that quality control during production is difficult to maintain.
On the other hand, the resistors for the measurement of temperatures including thin platinum layers have such advantages that:
The production process for resistors for the measurement of temperatures made using thin platinum layers is as follows: A thin platinum layer having a thickness of several thousands of angstroms is, first, attached to an insulating substrate by a vacuum evaporation method, sputtering, etc. The thin platinum layer is then finely patterned by a wet etching technique, a sputter etching technique, etc., followed by heating at a temperature of 800.degree.-1400.degree. C. in air. Then, trimming is carried out to adjust resistance, and the resulting product is cut into chips, to each of which lead wires are then connected, resulting in a resistor for the measurement of temperatures including a thin platinum layer. The insulating substrate is, for example, alumina, sapphire, silicon, or glass, each of which has the following advantages and drawbacks:
An alumina substrate is inexpensive and is excellent in the thermal resistance, and moreover has an excellent adhesion to platinum, but it is inferior in that problems arise with the formation of fine patterns due to the roughness of the surface thereof. If the surface is polished, it becomes smooth. However, polishing of an alumina substrate, which is hard, greatly raises the cost of the substrate. A sapphire substrate is excellent in thermal resistance, the adhesion to platinum and the smoothness of the surface, but it is inferior in that this substrate is most expensive and the operation of cutting it into minute chips is difficult. A silicon substrate is relatively inexpensive and smoothness of the surface thereof is excellent, and it is easy to be processed. However, when it is heat-treated, an alloy of the silicon and the platinum is formed, which affects the sensor characteristics thereof. A glass substrate is inexpensive, but presents problems such as having a poor adhesion to platinum and having no thermal resistance. Thus, all four of these substrates have disadvantages as well as advantages, and there is still a need for a better substrate.